Underwater projectile



March 25, 1969 J, (:filTCHER 3,434,425

UNDERWATER PROJECT ILE Filed June so, 1967 Sheet of 2 John L. Crifcher INVENTOR March 25, 1969 J R.THER 3,434,425

UNDERWATER PROJECTILE Filed June so, 1967 SheetiofZ John L. Crilcher INVENTOR United States Patent 3,434,425 UNDERWATER PROJECTILE John L. Critcher, Cockeysville, Md., assignor to AAI Corporation, Cockeysville, Md., a corporation of Maryland Filed June 30, 1967, Ser. No. 650,374 Int. Cl. F42b 19/32 US. Cl. 102-921 11 Claims ABSTRACT OF THE DISCLOSURE This invention relates to underwater projectiles, and particularly to an improved underwater projectile flechette type incorporating a particular configuration which maximizes velocity, range and target penetration, particularly in the depth range of up to 30 feet and the underwater visibility range at depths up to 30 feet.

In the prior art, various projectile arrangements have been employed for underwater ammunition, the most common being spear gun projectiles and shot shell power heads, as well as combined shot shell and spear projectiles. Such prior configurations have been substantially less than fully effective, due to such deficiencies as cumbersome size, limited velocity, limited effective range and small terminal energy for target penetration.

It is an object and feature of this invention to provide an underwater projectile of superior velocity, range and target penetration in Water depths of up to 30 feet and at ranges extending up to the effective visibility range at these depths.

Still other objects, features and attendant advantages will become apparent to one skilled in the art from a reading of the following detailed description of a single preferred embodiment constructed according to the invention, taken in conjunction with the accompanying drawings wherein:

FIGS. 1 and 2 are perspective views of a flechette projectile according to the invention.

FIG. 3 is a longitudinal side view of the projectile of FIGS. 1 and 2, with its stabilizing shroud in section for clarity of illustration.

FIG. 4 is a schematic sectional view of an underwater ammunition arrangement suitable for launching the underwater projectile of FIGS. 1 and 2 according to the invention.

FIG. 5 is a schematic representation of the projectile and cavitation envelope during flight of the projectile through water.

Referring now in detail to the figures of the drawings, the projectile 11 includes a cylindrical shaft or shank 13 having a frusto-conical nose section 15 with a flat tip end 15a, and a stabilizing tail section including canted stabilizing fins 17 and a stabilizing shroud 19.

The overall length B of the fins 17 is approximately four shaft diameters and the overall length A of the 'frusto-conical nose section 15 is approximately three and one-half shaft diameters.

The four stabilizing radial fins 17 are integrally formed with the shank 13, as by hot or cold metal working of the shank body to form the desired configuration, as through the medium of a suitable forming die. Surface 3,434,425 Patented Mar. 25, 1969 grinding of the radially outer surface of the fins may also be employed as necessary to effect the desired radial surface configuration. Each of the fins is preferably canted at an angle of approximately 2 with respect to the longitudinal axis of the shank 13. It will be appreciated that the canted fins 17 contribute to trajectory accuracy by imparting spin to the projectile, whereby for a given yaw angle the canted fin projectile dispersion is helical and has a smaller radius of error dispersion than that which would be obtained by a straight finned configuration with a unidirectional dispersion. The fins 17 are formed with an inclined forward face 17d and intermediate forward reduced span or diameter section 17:: of substantially constant diameter, and an enlarged span or diameter rear section 170 also of substantially constant span along its length. At the longitudinal junction of reduced span section 17a and enlarged diameter rear section 17c of each fin is a shoulder 17b against which is seated the thin-walled stabilizing shroud 19 which is press fit onto and about the reduced span section 17a of the fins 17. The leading edge of the circular band forming the sleeve shroud 19 is chamfered as indicated at 19a to reduce drag, and the enlarged span rear section 170 of the fins has an outer span substantially the same as the outer diameter of the sleeve shroud 19, thus providing a radially smooth continuation of this shroud surface at the junction therebetween the outside diameter and longitudinal length of the circular band forming the sleeve shroud 19 are each substantially equal to approximately one and one-third diameters of the shaft or shank 13.

The cone angle of the frusto-conical nose section 15 is 10 :l), included, and the flat tip end 15a of the frustrum is approximately .30 to .35 of the diameter of the shaft or shank 13.

The overall length of the projectile is equal to between 30 and 43 shaft diameters, with a preferred length of 43 diameters for minimum desired muzzle velocity of approximately 700 to 750 feet per second and associated launching propellant chamber pressures.

In one illustrative and preferred embodiment in which the shaft diameter is .100 inch, the band forming the sleeve shroud 19 has a thickness of .010 inch, and the length and outer diameter of the sleeve shroud 19 is .131 inch. Also, in this particular preferred embodiment, the projectile shank 13 is formed of tungsten and the circular band forming the sleeve shroud 1-7 is formed of heattreated steel for structural integrity, the overall weight being grains, and the overall length being 4.3 inches, with a frustrum cone angle of 10 and a tip diameter of .030 inch.

In operation, the launching velocity of the projectile is preferably near that of atmospheric pistol ammunition, being approximately 700 to 750 feet per second, and whereas drag forces render atmospheric bullet shapes and other flechette shapes inelfective in very short ranges under water, the present projectile is far superior in its range capability under water. The high mass per frontal area and specific nose and tail proportions contribute mutually to an efliciently low coefficient of drag, and the stability of the projectile flight is also maximized by the same balance of proportions.

In FIG. 4 is illustrated a suitable ammunition arrangement which may be employed for launching the underwater projectile according to the invention. In this arrangement, the projectile 11 is supported With its tail section 17, 19 cradled in a close fitting pocket formed in a pusher sabot 27, with the midsection of the shank 13 and nose section 15 supported respectively by frangible supporting and guiding units 23 and 25. The sabot'27 and supporting and guiding units 23 and 25 are slidably disposed in a bore 29 formed in a disposable barrel 21 which is closed and hermetically sealed against water entry at both ends, the forward end having a frangible removable closure cup 28 press fit in place, and the rear end behind the pusher sabot 27 having a closure head cap 24 threadedly secured in place and carrying a charger propellant 25 and a percussion primer 26 which may be suitably actuated by a firing pin 51. The disposable barrel may be removably inserted into a bore chamber formed in a cylinder 41, with the projectile 11 exiting through the frangible closure cup 28 and thereby achieving its maximum velocity before fully exiting from the air chamber formed within the bore 29 of the barrel 21.

In operation, as the projectile flies through the water the flat frustrum tip area 15a separates a bulk of water normal to the trajectory, creating a cavitation envelope CE of specific shape and length relative to the instant projectile velocity and depth. FIG. is illustrative of the cavitation envelope and the travel of the projectile through the water in depths of up to 30 feet and velocities up to 700 feet per second. The instantaneous cavitation envelope CE has an effective length extending well back of the rear finned section 17, 19 of the projectile 11, and may be of a length up to several times the projectile length, dependent upon depth and instant velocity, before pressure can close the cavity. The cavity is difficult to precisely measure and define in structural contents; however, evidence indicates that the forward area of the envelope surrounding the projectile body is composed of water vapor of varying density levels, the density gradient increasing at a high rate of change from the zone immediately adjacent the projectile body to the zone at the edge of the cavitation envelope, and the lines of equal vapor density extending in something of an arcuate form from the zone of the flat tip in a generally convex form along the length of the projectile and the remainder of the envelope rearwardly to the zone of closure where larger water droplets are forced into the envelope zone. It has been found that the density gradient of the water vapor WV increases so rapidly from the zone adjacent the projectile body that small increases of tail fin diameter or shroud diameter or projectile length, with respect to shaft diameter, cause very large increases in drag with resultant decrease in velocity and effective range and terminal energy of the projectile. The tail configuration 17, 19 raises a stabilizing force from collision with the vapor WV within the cavitation envelope, and as the water vapor WV thus exerts a drag force on the tail section at the same time, it will be appreciated that the tail section must be formed with the concept of minimizing contact with water vapor while insuring suflicient stabilizing force to accomplish stability or projectile flight. With the foregoing mentioned configuration and relative dimensions and weights, for muzzle velocities of approximately 700 feet per second and depths up to feet, the projectile is nearly free of boundary layer drag forces over its effective range except for the area of the frustrum fiat tip end 15a, and the very minute drag force exerted on the tail section 17, 19 by the low density water vapor in the central zone of the cavitation envelope cross section. The area of the flat tip end 15a is optimized for minimum drag and desired cavitational envelope vapor impingement for stability control on the tail section 17, 19, a frustrum tip end 15a of smaller proportion producing erratic flight with severe yaw resulting in negligible effective range, whereas increase in the proportions of the flat tip end 15a results in higher drag forces at this zone, which also decreases the effective range. In addition, it has been found that increases in the cone angle of the nose section 15, and/ or the diameter of the sleeve shroud 19 and fins 17 also results in higher drag forces which decrease the effective range, as will be apparent from considerations of the rapid radial increase in vapor density of the water vapor WV within the cavitation envelope. Use of fins 17 only without the shroud 19 results in excessive yawing and inaccurate flight of the projectile. It has further been found that reduction of the overall length relative to diameter and tip end area results in less momentum with proportionate loss in effective range, unless the launching velocity is increased inversely proportionate to the length reduction. In this respect, the preferred length of the overall projectile 11 has been found to be 43 diameters, and by a sacrifice of higher launching velocities and associated higher chamber pressures the length of the projectile has been successfully varied down to a length of 30 shaft diameters. It will, of course, be appreciated that such requirement for higher launching velocities and associated higher firing chamber pressures for launching the projectile put severe requirements upon the weight and strength of the launching ammunition arrangement and/ or barrel with consequent increase in bulkiness and the Weight of the equipment and decrease in efficiency of power utilization.

It has been found that the terminal efficiency of the remaining energy when the projectile is at a 30 foot range, which is the general visibility range in shallow water of up to 3 foot depth, equals approximately one-half that of the energy of the projectile at the launch location, and produces penetration force concentration of an extreme degree over a distance equal to and beyond this 30 foot visibility range. At the 30 foot depth the terminal efficiency of the remaining energy is about 25% of that of the launch location energy of the projectile, with consequent lesser but effective penetration force.

It will accordingly be appreciated that the critical interrelation of the various parameters of the projectile are effective overall to provide a highly desirable and useful underwater projectile which may be effectively used by underwater fishermen, divers, etc., with good results within the operating ranges of visibility in water depths up to 30 feet, and using launching velocities conventional to atmospheric pistol ammunition in the vicinity of 700 feet per second.

While the invention has been described with respect to a single illustrative and preferred embodiment, it will be apparent to those skilled in the art that various modifications may be made without departing from the scope and spirit of the invention. Accordingly it is to be understood that the invention is not to be limited by the illustrative embodiment, but only by the scope of the appended claims.

That which is claimed is:

1. A projected underwater projectile comprising:

a unitary one-piece long thin shaft having a substantially constant diameter cylindrical shank section, a frusto-conical forward nose section immediately adjoining said cylindrical shank section, and a finned tail section immediately adjoining said cylindrical shank section and having a forward portion of said fins of span substantially the same as the diameter of said shank,

said frusto-conical nose section having a blunt tip end with a diameter substantially one-third of the shank diameter for forming a drag-reducing cavitation envelope longer than said projectile during passage of said projectile through water,

said tail section having a plurality of radial fins formed thereon and canted with respect to the longitudinal axis of said shaft for imparting spin, and

a stabilizing sleeve shroud encompassing and secured about said fins and extending outwardly beyond the outer periphery of said cylindrical shank by an amount approximately the thickness of said sleeve shroud.

2. An underwater projectile according to claim 1,

the cone of said nose section being between approximately 9 to 11, and

said blunt tip end being flat.

3. An underwater projectile according to claim 2,

said nose cone angle being substantially 4. An underwater projectile according to claim 2,

said sleeve shroud having a drag-reducing chamfered forward edge,

said sleeve shroud having an outside diameter substantially equal to its length and equal to substantially 1 /3 shank diameters.

5. An underwater projectile according to claim 4,

said shaft having a length of between approximately 30 and 43 shank diameters.

6. An underwater projectile according to claim 4,

said shaft having a length of substantially 43 shank diameters.

7. An underwater projectile according to claim 5,

said fins having a length of approximately four shank diameters,

said sleeve shroud having its outer diameter and length equal to approximately 1 /3 shank diameters.

8. An underwater projectile according to claim 7,

said sleeve shroud having a thickness of approximately V of a shank diameter, and having a chamfered forward drag-reducing edge.

9. An underwater projectile according to claim 1,

each of said radial fins having a forward radially outer edge surface extending parallel with the axis of said shaft and a radially extending forwardly facing shoulder contiguous with and extending radially outward beyond said edge surface by an amount substantially equal to the thickness of said sleeve shroud,

said sleeve shroud being seated in press fit relation about and onto said parallel outer edge surface of said fins and in end-abutting relation against said shoulder.

10. An underwater projectile according to claim 9,

said fins each having a further radially outer edge surface extending rearwardly from said shoulder and having an effective envelope diameter at their forward end substantially equal to said constant diam eter cylindrical shank section and complementary to the inner diameter of said sleeve shroud, the eifective envelope diameter of the fins rearward of said shoulder being substantially equal to the outer diameter of said sleeve shroud.

11. An underwater projectile according to claim 10,

said fins being canted at an angle of approximately 2 to the shaft axis,

said shroud being disposed intermediate the forward and rear ends of said fins.

References Cited UNITED STATES PATENTS 2,965,028 12/1960 Woodward et a1. 102-7 3,141,434 6/1964 Van Billiard 114-20 3,323,457 6/1967 Biehl 10248 3,301,210 1/1967 Oeland 114-20 FOREIGN PATENTS 594,516 1 1/1947 Great Britain.

ROBERT F. STAHL, Primary Examiner.

US. Cl. X.R. 

